1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly, to methods of optimizing a recording current according to an operating environment temperature, and setting tracks per inch (TPI), or recording density, in consideration of the adjacent track erasure (ATE) characteristics of a head.
2. Description of the Related Art
A hard disk drive is a recording device used to store information. In general, tracks are concentric circles formed on a recording surface of a magnetic recording disc, and information is recorded on at least one track. In the hard disk drive, a disk is rotated with respect to a spindle motor, and information is accessed by a read/write unit built in an actuator arm that is rotated by a voice coil motor. The voice coil motor is excited by an electric current, rotates the actuator arm, and moves a write/read head. The write/read head senses a change in magnetism generated on the surface of the disk, and reads information from the recording surface of the disk. An electric current is supplied to the head to record information on a data track. The supplied electric current generates magnetism and the magnetism magnetizes a portion of the recording surface of the disc.
Recording density can be increased by increasing a density of track, (Track Per Inch; TPI) and by decreasing a flying height (FH) of a head. However increase of TPI and decrease of FH may cause erasure of data recorded on a track adjacent to a target track due to the magnetism generated by the magnetic recording head. Such a phenomenon is called adjacent track erasure (ATE). The ATE becomes important when a recording current generated by the head is excessively high. However, the recording performance of the hard disk drive deteriorates when the recording current is insufficiently supplied.
Meanwhile, as hard disk drives have been developed to have a high capacity, or high density, the TPI has been required to increase, thereby causing track width to become narrower, and thus, recording control performance needs to be improved to adjust a recording width of the magnetic head, and reduce noise produced by the magnetic head.
U.S. Pat. No. 6,101,053 discloses a method of setting a write condition by recording data on m+1th and m−1th tracks of a disk by a specific offset, measuring the rate of errors in data recorded on an mth track, and setting tracks per inch (TPI) to adjust the rate of errors to a desired level. However, this method is not capable of preventing ATE of a head caused by a level of a write current, which is a portion of the recording current, as will be explained later.
Conventionally, the recording current is optimized in consideration of the degree of ATE of a head during a burn-in test process of a hard disk drive.
To prevent ATE, the level of the write current is reduced through adaptive read channel optimization (ARCO) in a hard disk drive, for respective data zones of a disk, or according to temperature.
In general, during manufacture of hard disk drives, adjacent track writing (ATW) is performed several hundred or several thousand times, to adjust heads undergoing ATE. In general, during manufacture of a hard disk drive, processes such as a servo write process, a functional test, and a burn-in test are sequentially performed. The servo write process records location information on a disk. The functional test checks whether a maintenance cylinder has defects or whether a read/write operation can be satisfactorily performed in a data zone of a disc. The burn-in test carries out optimization of a read channel and optimization of a write channel of the hard disk drive. The optimization of the read and write channels is performed by a controller included in the hard disk drive.
More specifically, the coercivity of the hard disk is varied according to a temperature. The coercivity is decreased at high temperature and increased at low temperature.
To solve this problem, conventionally, the write current (WC) or an overshoot current (OSC) (which, as previously mentioned, is part of the recording current) in the hard disk drive is optimized according to the temperature of the hard disk drive. More specifically, the WC or the OSC is increased to reduce the coercivity of the hard disk drive at low temperatures. Similarly, the WC or OSC is reduced to increase the coercivity.
But the conventional optimization of the recording current is disadvantageous, in that the recording current is optimized at a room temperature during the burn-in process, and the write current is uniformly increased or reduced to a predetermined level at environmental conditions during use, e.g., a high-temperature mode and a low-temperature mode. That is, since the recording current is not optimized in consideration of the characteristics of the head, the write current may be increased or reduced to an undesirable level, and cause deterioration of the performance of the hard disk drive.
In particular, the conventional optimization of the recording current does not consider thermal pole tip protrusion (TPTP) affected by a level of the OSC. Accordingly, when conventional optimization is applied to a head of a high-degree TPTP, the level of the WC or the OSC become excessively high or low, and thus a head/disk interface (hereinafter referred to as “HDI”) worsens. The deterioration of HDI is likely to cause many problems, such as damage to the head, thermal asperity (TA), and a reduction in altitude margin (marginal change due to a change in the FH of the head due to a change in an atmospheric pressure).